The invention relates to a set for creating an offset-resurfacing hip-joint implant. This is understood to be a surface replacement for the natural sliding or articulating surfaces of the acetabulum and the hip-joint head.
So-called cap implants, which are placed over the prepared, natural remaining joint head and which can then be fixed in this position, are being used more and more in recent years. Cap implants comprise a cap, which has an outer shape patterned to the natural joint ball and which can be placed on a (partially) prepared, natural remaining joint head. Such an implant can be created from the so-called set for creating a reinforcement implant according to German Patent DE 102 18 801.
A prerequisite for a stable secondary fixation is stable bone material of the remaining bone. For example, in the already mentioned patent it is proposed to couple a peg to the joint head cap, wherein this peg is set in a corresponding milled section in the femoral neck. This peg has a surface, which is provided with a three-dimensional, open-mesh spatial network structure, in which and through which bone trabeculae of the surrounding bone material grow and provide for the stable secondary fixation.
There are, however, indications, in which one can still refrain from milling the femoral neck in order to create space for the peg. Here, the so-called Legg-Calve-Perthes disease is to be mentioned, which causes aseptic bone necrosis on one or both sides in the region of the femur head epiphysis. This disease appears primarily in boys of ages from 4 to 12 years old (Pschyrembel, Klinisches Wörterbuch [Clinical Dictionary], 259th edition, page 1285 (2002)). Healing without deformation is indeed possible, but a possible roller or mushroom shape of the femur head with flattening of the acetabulum, more rarely coxa plana or arthrosis deformans, remains.
Another indication, for example, is a cyst in the hip-joint head, which leads to surface defects of the joint head.
Very generally, necrosis of the joint head can lead to surface defects, which, however, does not always justify the complete resection of the joint head and the accommodation of the patient with a short-stem endoprosthesis (European Patent EP 0 878 176).
In principle—and this has been increasingly recognized in recent times—it is favorable to hold off (partial) resections of bones as long as possible, in order to be able to revert back to several steps of the endoprosthetic accommodation, if a revision surgery from the short-stem endoprosthesis to the classic long-stem endoprosthesis is needed at a later time. The use of the latter endoprosthesis requires the complete resection of the femoral neck.
With a resurfacing hip implant according to German Patent DE 10 2005 011 361, a proposal has been made, which enables the greatest possible flexibility with respect to long-term preservation of the implant in situ, that is, it helps to delay an extensive endoprosthetic accommodation.
This has been realized by a set for creating a resurfacing hip implant, which has a 1 to 1.5 mm thick metallic shell for cemented insertion into the natural acetabulum, from which only cartilage has been removed, as well as a 1 to 1.5 mm thick metallic cap for cemented placement on the natural hip-joint head, from which only cartilage has been removed, and in addition an inlay having a material thickness between 2 to 5 mm, which can be inserted into the acetabulum shell as a sliding partner for the hip-joint head cap.
Both the osseous acetabulum and also the osseous hip-joint head are here processed with a profile cutter, as is the case for implanting a total hip-joint replacement implant. The acetabulum and joint head are merely freed from cartilage and connective tissue, i.e., cartilage is removed.
This implant has proven itself in practice. However, there are indications, in which defective positions in the head must be compensated. This can be the case after a trauma or else due to advanced wear.